Dot probe experiment:

Hi all,

I have a serious problem I can not resolve on my own. Here you will find a description from the experimental design (a modified dot probe paradigm), and the Superlab files (4.08) and stimuli are attached.

Each object (H, S, or M) will be presented twice (together with a circle or a square), for a total of 48 trials. On each trial, a blank screen appears for 200 ms, followed by a central fixation symbol (*) for 100 ms. Next, this symbol will be replaced by an object (H, S, or M) in one of four screen quadrants. After 500 ms, these objects will be replaced by a shape (circle or a square) which appears either in the same quadrant as the photograph (filler trials; 25% of total) or in a different quadrant (experimental trials; 75% of total) and remained until a response was given (in this sample experiment “participants” do not need to response to facilitate the tests).

So far nearly everything works: all stimuli (objects: H, S, or M and shape: circle or square) appear equal often in the four screen quadrants (trial variables: random with no replacement). One problem remains: how can I ensure, that objects and shape are on the same location on the screen?

Please take a look at the experiment attached:
in 25% (= 2) cases should be the trial variables look like this
loc_h = loc_circle_h
loc_h = loc_square_h

loc_m = loc_circle_m
loc_m = loc_square_m

loc_s = loc_circle_s
loc_s = loc_square_s

Any suggestions?

Sascha (227 KB)

I’m a little unclear on one aspect: do you want the shape to always appear in the same position as the image?

No (this would be easy to setup: simply use the same trial variable for shape and image). I want the shape to appear on the same position as the image only in 25% of the trials …

No reply … Is this design possible with Superlab?

A colleague and I have spent some time trying to make the shape appear as you want in only 25% of the trials. Unfortunately, we were unable to come up with the correct percentage. I have posted the experiment that we worked on, so you can see how we went about it. We simplified the experiment down to only 2 trials, I hope this is helpful.

Sasha.Exp1.01 rev G.sl4 (7.48 KB)